1. Field of the Invention
The present invention relates to a field of an organic light-emitting diode and a fabrication method thereof. More specifically, the present invention relates to a high-molecule-based organic light-emitting diode and a fabrication method thereof.
2. Description of Related Art
Organic light-emitting diodes (OLEDs) are increasingly attracting interest because of their great potential as high-quality flat-panel displays and for liquid-crystal-display backlighting and solid state illumination applications. To replace current display and illumination technologies, and to make the resultant products more energy-saving and last longer, OLEDs with higher power efficiency are demanded. A high efficiency device must possess properties of low carrier-injection-barrier, high carrier mobility, excellent carrier- and exciton-confinement, effective exciton-generation on host, efficient host-guest energy-transfer, balanced carrier-injection and high self-luminescent materials. The use of phosphorescent materials is an important strategy to obtain high-efficiency OLEDs, because they allow for the simultaneous harvesting of both singlet and triplet excitons, achieving nearly 100% internal quantum efficiency. Moreover, the phosphorescent materials must be morphologically stable during fabrication and operation. This fact, on the other hand, has revealed one drawback frequently encountered when employing hosts with low molecular weight that the resultant film integrity may be easily damaged owing to the inherently low glass-transition temperature. As a result, the ideal host molecules, if not polymeric, should be ones with high molecular weight, such as a host molecule, 3,5-di(9H-carbazol-9-yl)tetraphenylsilane, recorded in US Patent No. 2007/0173657.
Furthermore, long lifetime molecular-based organic electronics, such as OLEDs, organic solar cells, organic transistors, organic sensors, organic memories and etc, inevitably demand their constituent molecules to be highly thermal-stable. Polymer materials exhibit varied molecular-weight and are not easy to be purified, causing the resultant devices to commonly exhibit a lower efficiency. In contrary, small molecular materials possess high electroluminescent efficiency but their low molecular weights would cause weak mechanical strength of the film integrity. Coupling with the special needs in molecular design, this will inevitably result in an increase in molecular weight.
However, the increased molecular weight would in turn make the resultant molecules difficult to deposit by using a vacuum evaporation method, while using a solution-process would frequently result in undesired relatively poorer efficiency. As a result, it is necessary to provide an OLED capable of having molecular materials and high efficiency.